This invention relates to structures for use in supporting concrete reinforcing bars while the concrete is poured. Structures of this nature are well known and commonly referred to as "chairs". They are used, for example, in forming concrete slabs and the like where, for example, reinforcing bars are to be supported above a base surface onto which the concrete is poured to form a slab, so that the reinforcing bars become embedded in the slab between the base surface and the top of the slab. The procedure is that prior to pouring the concrete, the reinforcement is supported above the base surface on an array of chairs so that when the concrete is poured both the reinforcing bars and the chairs become embedded in the slab.